The present invention relates to methods of recording a neural response following stimulation of neural tissue. More specifically, the present invention relates to methods for measuring and processing neural responses that minimize stimulus artifacts and system noise.
Modern neural stimulators have the capability of measuring the effectiveness of electrical stimulation of a nerve tissue. This involves delivering a stimulus to a nerve through a stimulating electrode and recording the electrical response, as the nerve depolarizes and repolarizes, using a recording electrode. Such recording and capturing of nerve electrical activity is termed neural response imaging (“NRI”).
Obtaining such a neural response (“NR”) is important clinically for determining whether stimulation of nerves is occurring at a given stimulus setting and also for determining optimal stimulation parameters for each electrode or electrode configuration.
High quality responses are often difficult to obtain because the neural recordings can be marred by the presence of stimulus artifacts, i.e., the neural recording records the voltage potential of the stimulus pulse and may obscure the desired NR signal. Another source of recording artifact is cross-talk between the recording circuit and the stimulation circuit. When the recording system is built into a small implantable system, such as an implantable cochear stimulator or a spinal cord stimulator, the stimulation and recording circuits are necessarily placed very close to each other within the stimulator and, hence, cross-talk can develop between the two circuits.
One method of reducing the stimulus artifact and cross-talk and extracting an NR is to use a forward masking technique. Unfortunately, the conventional forward masking paradigm often leaves large residual artifacts, because the paradigm assumes linearity and non-hysteresis of the system response. The hysteresis leads to a response to the probe following the masker to have an artifact which is different from the response to the probe alone, resulting in a residual artifact.
Accordingly, what is needed is an improved method of recording and processing neural responses, which method is not dependent on system linearity.